add #include guard hack

According to MSVC manual (*1), cl.exe can skip including a header file
when that:

- contains #pragma once, or
- starts with #ifndef, or
- starts with #if ! defined.

GCC has a similar trick (*2), but it acts more stricter (e. g. there
must be _no tokens_ outside of #ifndef...#endif).

Sun C lacked #pragma once for a looong time.  Oracle Developer Studio
12.5 finally implemented it, but we cannot assume such recent version.

This changeset modifies header files so that each of them include
strictly one #ifndef...#endif.  I believe this is the most portable way
to trigger compiler optimizations. [Bug #16770]

*1: https://docs.microsoft.com/en-us/cpp/preprocessor/once
*2: https://gcc.gnu.org/onlinedocs/cppinternals/Guard-Macros.html

1 files changed, 13 insertions, 0 deletions

diff --git a/vm_callinfo.h b/vm_callinfo.h
index b3de14dcab..8b575f11c6 100644
--- a/vm_callinfo.h
+++ b/vm_callinfo.h
@@ -1,3 +1,14 @@
+#ifndef RUBY_VM_CALLINFO_H                               /*-*-C-*-vi:se ft=c:*/
+#define RUBY_VM_CALLINFO_H
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ */
+
 #include "debug_counter.h"
 
 enum vm_call_flag_bits {
@@ -426,3 +437,5 @@ vm_ccs_p(const struct rb_class_cc_entries *ccs)
 
 // gc.c
 void rb_vm_ccs_free(struct rb_class_cc_entries *ccs);
+
+#endif /* RUBY_VM_CALLINFO_H */